Magnetic RAM a.k.a Magnetoresistive Random Access Memory By: Ashley Jefferson What is Magnetic RAM? MRAM is memory technology that uses electron spin to store information Unlike conventional RAM chip technologies, data is not stored as electric charge or current flows, but by magnetic storage elements. Magnetic RAM Architecture Shows how MRAM reads and writes Credit: http://domino.research.ibm.com What is Magnetic RAM? How does it work? An MRAM chip is made up of millions of pairs of tiny ferromagnetic plates (like the one covering hard drives) called memory cells, i.e., magnetic sandwiches consisting of two magnetic layers separated by a very thin insulating layer One of the two plates is a permanent magnet set to a particular polarity, the other's field will change to match that of an external field. A memory device is built from a grid of such "cells". An image of the layers involved in an MRAM storage device. Credit: http://domino.research.ibm.com How does it work? MRAM works like the read/write head of a hard drive. But unlike a hard drive, which includes mechanical parts (the moving arm holding the read/write head and the rotating plates on which the information is stored), MRAM is a solid state device and, as such, has much greater speed and durability How does it Read? An MRAM chip reads information by measuring the electrical resistance of a specific cell that, in turn, depends upon the alignment of the magnetic moments of the layers of the cell. To read a bit of information, a current is passed through the memory cell. If the magnetic moments are in a parallel orientation, then the detected resistance would be smaller than if they were in an anti-parallel orientation. Diagram of Read Process Credit: http://www.tfot.info/ How does it Write? Write is achieved by the alignment of the magnetic moments of the two memory layers into one or the other relative orientation. Current is passed through two sets of parallel wires or write lines (called a bit line and a digit or word line), which pass over and beneath the memory cells, respectively To write to a particular memory cell (bit), current is passed through the two wires that intersect at that memory cell. Diagram of Write Process Credit: http://www.tfot.info/ Advantages of Magnetic RAM MRAM has been called the “ideal memory”- potentially combining the density of DRAM with the speed of SRAM and non-volatility of Flash memory or hard disk, and all the while consuming a very low amount of energy MRAM has much faster write speeds than Flash and has an unlimited endurance, meaning that MRAM is not subject to the degradation suffered by Flash. Advantages of MRAM MRAM can resist high radiation, and can operate in extreme temperature conditions. It is likely that we’ll see the first MRAM in applications that need such properties Like Flash, MRAM retains data after a power supply is cut off, potentially eliminating that seemingly endless boot time of conventional computers when data from the hard drive is transferred to RAM, as well as loss of data when the computer is suddenly shut off. Advantages of MRAM The magnetic architecture of the chip can be reprogrammed on a whim and its adaptability could make it very popular with manufacturers of special- purpose computing hardware, from video-game platforms to medical diagnostic equipment. The chip's nanomagnets -- on the order of 110 nanometers wide -- can be assembled into arrays that mirror the function of transistor-based logic gates in addition to storing information. These logic gates are the building blocks of computer technology, giving microchips the power to process the endless rivers of binary code. Advantages of MRAM Using a magnetic state for storage has two main benefits: – 1) the magnetic polarization does not leak away with time like charge does, so the information is stored even when the power is turned off; and – 2) switching the magnetic polarization between the two states does not involve actual movement of electrons or atoms and thus has no known wear-out mechanism. Disadvantages of Magnetic RAM Is (currently) expensive Power consumption of MRAM technology is still high Freescale’s MRAM technology only holds 4M. So it can’t currently be widely used Comparison Table Credit: http://www.tfot.info/ What is MRAM going to be used for? Proposed uses for MRAM include devices such as: – Aerospace and military systems – Digital Cameras – Notebooks – Smart Cards – Mobile Telephones – Cellular base stations – Personal Computers Is it available today? Although MRAM has many advantages over virtually every existing memory type, it is still in its infancy. Many had hoped MRAM would usher in the age of instant-on computers able to replace the computer main memory and hard drives, but, due mainly to its cost, these hopes remain a dream Even though many large companies such as IBM, Intel and HP, are working on MRAM, Only two vendors have succeeded in bringing MRAM parts to the mass market - Cypress and Freescale. Cypress, however, has discontinued their offering shortly after release Is it available today? In February, Toshiba and NEC announced a 16 Mbit MRAM chip with a new "power-forking" design. It achieves a transfer rate of 200 MB/s, with a 34 ns cycle time - the best performance of any MRAM chip. It also boasts the smallest physical size in its class -- 78.5 square millimeters -- and a low power requirement of 1.8 volts. In July 2006, Freescale started selling the first commercial MRAM module, with 4Mbit of memory, for $25 a piece. This is still very expensive and low density, and probably suits a very small list of select customers. A realistic timeframe for a cell phone with MRAM or a MRAM-Disk-On-Key is probably 2010 at least.